On 13 May 1758, England. The 2nd Battalion of the 19th Foot was converted into a new Regiment, the 66th.
The new Regiment had nine companies including a Grenadier company. This Regiment played no active part in the Seven Years War.
Three companies were deployed at Berwick, two at Alnwick and one at Shields.
During 1760, Ireland, Carrickfergus. 1200 French, under General Thurot landed at Carrickfergus. 130 men of the 62nd defended a ruined castle against the French through three assaults. After the Colonel (Jennings) was wounded, the detachment, suffering heavy loss, and out of ammunition, surrendered. The French granted Honours of war, and prisoners of war on parole rights, until exchanged. A vote of thanks was received from the Irish House of Commons
During Feb 1760, England, Portsmouth. A draft of 574 was detailed to go to Portsmouth and the whole of the Regiment was marched there to see the draft off. The remains of the Regiment then marched to Frome, where three companies were deployed and Bradford on Avon, where another three companies were deployed and one company at Bruton.
During Apr 1760, West Indies, Jamaica, Port Royal. Companies of the Regiment stationed at Port Royal, Jamaica were used to suppress a negro insurrection. One of the last battles of importance was at a place called Bagnal's and the 49th almost certainly played a part in this
During Dec 1760, England, Trowbridge. Two companies deployed here and, in January 1761, the Regiment returned here with detachments sent out to Bruton, Shepton Mallet and to Bradford-on-Avon, where the detachment was needed to control riotous assemblies.
During 1762, West Indies, Jamaica, Spanish Town. During 1762 the Regiment was deployed to various places:
Five companies deployed to Jamaica, Spanish Town
One company deployed to Jamaica, Port Ontario
One company deployed to Jamaica, Montego Bay
One company deployed to Jamaica, Mitcham
One company deployed to Jamaica, Kingston
One company deployed to Jamaica, Old Harbour
One company deployed to Jamaica, Negro Town
One company deployed to Jamaica, Black River
One company deployed to St Lucia
On 20 Apr 1762, West Indies, Guatemala, Mosquito Coast. Governor Lyttleton writes he has sent Captain Joseph Otway of the 49th to the Mosquito Coast apparently as a subordinate to Captain Hodgson, who was then in Honduras